1. Field of the Invention
This invention relates to an information processing apparatus for reproducing the information recorded on a recording medium such as an optical disk with recording tracks, and more particularly to an information processing apparatus capable of an improved seek operation.
2. Description of the Related Art
Optical-disk apparatuses have been put to practical use which record and reproduce information on and from an optical disk with recording tracks by means of laser light emitted from a semiconductor laser provided on an optical head.
In such optical-disk apparatuses, the optical head is moved radially across the optical disk, or so as to cross tracks, by means of a linear motor. The movement of the optical head by the linear motor causes a spot of laser light to move to a target track. In some optical-disk apparatuses, when the optical head has approached the target track, the moving velocity (hereinafter, referred to as the velocity) of the optical head is controlled according to the decelerating reference speed data, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 1-271921.
In the case of the above-mentioned type of apparatus, a velocity control system for controlling the velocity of an optical head is designed to decrease the velocity of the optical head as the light spot approaches the target track. The velocity trajectory (or the target velocity which is designed for the optical head to move along) itself designed to include the decelerating velocity data is referred to for the reference velocity during a seek operation. In this case, at the time when the light spot has reached the target track, the velocity of the light spot must be sufficiently slow so that a tracking operation (i.e., the operation of centralizing the light spot on the track) can be effected reliably.
However, since in such an optical disk apparatus, the control band of the velocity control system (or the response characteristic) has a finite value, there arises the velocity deviation of the actual velocity of the optical head from the reference speed (equal to the velocity trajectory) during deceleration. Specifically, because the optical head's actual velocity is greater than the reference velocity, the optical head's velocity has not become sufficiently low when the head has reached the target track. As a result, in the prior art, the head has sometimes failed to switch over to a tracking operation. Consequently, it has been difficult to shorten the moving (seek) time of the optical head. To reduce the velocity deviation described above, for example, disturbance tolerance servo systems for optical disk drives have the structure of a two-degrees-of-freedom control system where a feedforward section and a phase-delay compensation section are added to a conventional gain compensation section, as disclosed in "A Collection of Papers Read in the Lecture Given in the Information, Intelligence, and Precision Equipment Division of the Mechanics Society of Japan [No. 920-67] IIP'," Tokyo, Oct. 20-21, 1992. Since many branches and junctions of signal paths are required in the velocity control system, this approach, however, has the disadvantages of making the control system complex and consequently increasing the cost of putting the product to practical use.